Method of driving passive matrix liquid crystal display

ABSTRACT

Driving is effected by MLA under a condition of L≠M or (M/L·(L+D) )≠N where M represents the total number of row electrodes, L represents the number of simultaneously selected row electrodes, D represents the number of dummy row electrodes and N represents the maximum magnifying power of a column voltage wherein driving is performed at a driving bias ratio which is deviated toward the minimum bias ratio with respect to the optimum bias ratio.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for driving a simple matrixliquid crystal display device comprising a plurality of liquid crystalelements each being provided in correspondence with each pixel and aplurality of row electrodes and column electrodes for driving the liquidcrystal elements by a super-twisted nematic system (hereinbelow,referred to as a STN system) wherein predetermined voltages are appliedto the electrodes to control each liquid crystal element so as toproduce brightness in response to an effective value of applied voltagewhereby a predetermined picture image is displayed on a display areawhich is comprised of a matrix of the liquid crystal elements. Inparticular, the present invention relates to a method for driving asimple matrix liquid crystal display device which is capable of reducingvoltage for driving the display device.

2. Discussion of the Background

Conventionally, as methods for driving a simple matrix liquid crystaldisplay device provided with electrodes used commonly for a plurality ofliquid crystal elements, there are a driving system based mainly on aso-called line successive driving system and a driving system basedmainly on a multiple line addressing driving system (or it is called aMLA system).

The line successive driving system is a driving system in whichpredetermined voltages are successively applied to electrodes of everyrow, and at the same time, predetermined voltages are applied to aplurality of column electrodes whereby control voltages are applied tothe row electrodes. Then, each of the liquid crystal elements iscontrolled to have a transmittance in response to an average effectivevoltage applied during a time in which the voltages are once applied toall the row electrodes (hereinbelow, referred to as a frame). Apredetermined picture image is displayed for each frame period.

The MLA driving system is a driving system in which all the rowelectrodes constituting a display picture area are divided intosubgroups each comprising a plurality of row electrodes (asimultaneously selected number), and predetermined voltages are appliedto row electrodes for each subgroup and at the same time, predeterminedvoltages are applied to a plurality of column electrodes wherein theabove-mentioned operation is repeated at least the same number of timesas the simultaneously selected number to all the subgroups. Thus, eachof the liquid crystal elements is controlled to have a transmittance inresponse to an average effective voltage applied during a time in whichthe above repetitive operations are finished (it is called a frameperiod), and a displayed picture image is formed in each frame period.Such MLA system is disclosed in Japanese Unexamined Patent PublicationJP-A-6-27907, U.S. Pat. No. 5,262,881 and Japanese Unexamined PatentPublication JP-A-8-234164 and so on.

In the MLA driving system, when predetermined voltages aresimultaneously applied to a plurality of row electrodes, the voltagesapplied to the column electrodes are the product of a unit columnvoltage and values obtained by performing calculation of a plurality ofdisplay data at the intersections of column electrodes and rowelectrodes and column data of orthogonal matrix used for applying thescanning voltages. The maximum value of magnifying power obtained by thematrix calculation suffers restriction by an orthogonal matrix used forthe calculation, and it takes at most a value of the number of rows inthe matrix.

The liquid crystal display device has been used as a display device fora man-machine interface with the progress of highly intelligent society.In recent years, it is widely used not only for a desktop type personalcomputer but also for a notebook type personal computer, PDA (a portableinformation terminal) or a portable telephone, which is suitable forcarrying, taking an advantage of thin and light in weight. As a result,the development of the liquid crystal display device tends to increasethe surface area of the screen as well as improvements in reduction ofthe weight and low power consumption.

In such liquid crystal display device, various measures have been takento lower the power consumption rate. In more detail, there are measuresto form a liquid crystal element capable of responding to a loweffective voltage or to use a reflection type liquid crystal elementwithout requiring a back light. Further, there is published“General-purpose addressing technology for an effective value responsetype liquid crystal display device (SID, a record of a meeting of SIDinternational display research society 1988, p. 80-p. 85)” as papers forreporting the relation between a driving method for such liquid crystaldisplay device and electric power consumption. The papers report thatwhen a multiple line driving is performed under conditions thatL={square root over (M)} (where M represents the total number of rowelectrodes for a display area and L represents a simultaneously selectedmember) and the optimum bias ratio at which a ratio of an effectivevoltage versus a ratio between an effective voltage in an ON displaytime and an effective voltage in an OFF display time becomes the maximumis used, a driving voltage for the liquid crystal display device can bereduced in comparison with a case of using the line successive drivingsystem.

The conventional liquid crystal display device uses a lithium ionbattery (a button battery) of relatively high voltage (about 3.3 V) andreduced weight. However, the display device requires a driving voltageof 7-9 V even though an improvement of a liquid crystal material hasbeen made, and accordingly, there is a voltage increase of about 3times. As a result, there caused power loss due to a voltage increasecircuit, which was against an attempt to lower consumption power. Thus,it was impossible to achieve the purpose of lowering consumption powerto an extent of a sufficient utility. Further, since such voltageincrease circuit required a fairly high breakdown strength, a generallyutilized 5 V standard logic process device, which has generally beenused, could not be used to increase a degree of integration.Accordingly, a logic process for inclusive use had to be developed toincrease a degree of integration. As a result, there is resulted anincrease of cost for the liquid crystal display device including adriving device and a prolonged term in designing. Further, there wereproblems of causing an additional cost in changing designing anddifficulty in responding a demand of multi-item-small-production.

In forming actually the voltage increase circuit, there is a problemthat the effective voltage changes due to the temperature dependence ofliquid crystal whereby it is impossible to apply predetermined columnvoltages and row voltages. Accordingly, it is necessary to determine avoltage increase level in consideration of a temperature for the liquidcrystal. However, working voltages to the liquid crystal itself are aptto vary under the above-mentioned condition. Accordingly, it wasnecessary to determine a voltage increase level with a larger margin soas to assure operating performance in a low temperature region. Thiscreated a cause of an increased power consumption rate by the provisionof the voltage increase circuit as an addition circuit.

Further, besides the temperature dependence of the driving voltage, theresponse speed of liquid crystal becomes high in a high temperatureregion in a liquid crystal display for providing display data of staticimages, and there causes reduction of the contrast due to the frameresponse inherent to the passive matrix, whereby a phenomenon whichdeteriorates visibility takes place. Recently, there is a demand for asmall or middle type liquid crystal devices having the performancecapable of sequentially displaying cuts of images or scrolling of imagesof letters regardless of a high temperature region, which inevitablyreduces visibility even in a static image with the tendency that liquidcrystal material becomes quickly responsive. In order to respond suchdemands, it is necessary to increase a driving frequency for the liquidcrystal device to thereby prevent a reduction of contrast ratio resultedfrom the frame response. However the power consumption rate of theliquid crystal display device tends to increase with an increase of thedriving frequency. Such poor operational environments create a factorthat the device does not have a sufficient utility.

SUMMARY OF THE INVENTION

As a result of extensive study to eliminate the above-mentionedproblems, the inventors of the present invention have found that when aMLA driving is used against the reduction of visibility and the MLAdriving is performed under a condition of L≠{square root over (M)}, avoltage difference is produced between the maximum column voltage androw voltage at the optimum bias ratio at which an effective voltageratio in an ON display time and an OFF display time becomes the maximum,and that in a graph having an abscissa which represents the ratio of aneffective voltage in an ON display time to an effective voltage in anOFF display time and an ordinate which represents a driving voltagenecessary to drive the liquid crystal elements, when one of the maximumcolumn voltage and the scanning voltage is increased, the other isdecreased wherein the maximum column voltage coincides with the scanningvoltage at a bias ratio other than the maximum bias ratio, and at whichpoint, the driving voltage becomes the minimum and there exists theminimum bias ratio which is lower than the driving voltage at the timeof the optimum bias, and thus, the present invention has beenaccomplished.

It is an object of the present invention to provide a method for drivinga simple matrix liquid crystal display device, which can reduce a powerconsumption rate in comparison with a driving method using theconventional MLA driving system while the ratio of an effective voltagein an ON display time to an effective voltage in an OFF display time canbe assured.

Further, it is an object of the present invention to provide a methodfor driving a simple matrix liquid crystal display device, which can bedriven practically by using a battery such as a button battery and whichcan increase a degree of integration for a driving circuit for theliquid crystal display device by using a standard logic process device.

In accordance with the first aspect of the present invention, a multipleline addressing driving is effected with an L number of simultaneouslyselected row electrodes to provide L≠{square root over (M)} where Mrepresents the total number of row electrodes for driving a display areaand L represents the number of simultaneously selected row electrodes,wherein driving is performed at a bias ratio which is deviated towardthe minimum bias ratio at which a driving voltage is the minimum withrespect to the optimum bias ratio B_(OPT) at which a ratio of aneffective voltage value in an ON display time to an effective voltagevalue in an OFF display time is the maximum.

According to the second aspect of the present invention, in theabove-mentioned first aspect, the display area is divided into subgroupseach comprising L lines; column elements selected in an orthogonalmatrix of L lines composed of +1 and −1 are made corresponding to eachline of the subgroups; row voltage levels where +1 corresponds to +VRand −1 corresponds to −VR are applied to each row electrode of thesubgroups; inner products are obtained from an L number of column dataelements, having a value −1 in an ON display time or +1 in an OFF time,which intersect a certain row electrode and column elements in theorthogonal matrix of L lines; predetermined column voltages inproportion to the inner products are applied to the column electrodes insynchronism with the row electrodes, and a bias ratio B_(X) given byVR/VC where VC represents the maximum column voltage satisfies1≦B_(X)<B_(OPT).

According to the third aspect of the present invention, in the first orsecond aspect, 0.3{square root over (M)}≦L≦2{square root over (M)} and0.3B_(OPT)≦B_(X)≦0.9B_(OPT) are satisfied.

According to the fourth aspect of the present invention, in the first orsecond aspect, 40≦M≦100 and B_(X)≦0.7B_(OPT) are satisfied.

According to the fifth aspect of the present invention, in the first orsecond aspect, B_(X)=1 is satisfied.

According to the sixth aspect of the present invention, in the first,second, third, fourth or fifth aspect, M=20-40 and L=4 are satisfied.

In accordance with the seventh aspect of the present invention, amultiple line addressing driving is effected with an L number ofsimultaneously selected row electrodes to provide {square root over((M/L·(L+D)))}≠N where M represents the total number of row electrodesfor driving a display area, L represents the number of simultaneouslyselected row electrodes, D represents the number of dummy row electrodesand N represents the maximum magnifying power of a unit column voltageobtained by a predetermined matrix calculation based on display data andscanning voltages applied to the row electrodes, wherein driving isperformed at a driving bias ratio which is deviated toward the minimumbias ratio at which a driving voltage is the minimum with respect to theoptimum bias ratio B_(OPT) at which a ratio of an effective voltagevalue in an ON display time to an effective voltage value in an OFFdisplay time is the maximum.

According to the eighth aspect of the present invention, in the seventhaspect, the display area is divided into subgroups each comprising Llines; column elements selected in an orthogonal matrix of L+D linescomposed of +1 and −1 are made corresponding to each line of thesubgroups; row voltage levels where +1 corresponds to +VR and −1corresponds to −VR are applied to each row electrode of the subgroups;an L number of column data elements intersecting a certain row electrodeare represented as −1 in an ON display time or +1 in an OFF time and a Dnumber of dummy data are made corresponding to column data elements toprepare an L+D number of column data elements; inner products areobtained from such column data elements and column elements in theorthogonal matrix of L+D lines; predetermined column voltages inproportion to the inner products are applied to the column electrodes insynchronism with the row electrodes, L which satisfies {square root over((M/L·(L+D)))}≠N where N represents the maximum value of the innerproducts is used, and a bias ratio B_(X) given by VR/VC where VCrepresents the maximum column voltage satisfies 1≦B_(X)<B_(OPT).

According to the ninth aspect of the present invention, in the seventhor eighth aspect, 0.3{square root over (M)}≦L+D≦2{square root over (M)}and 0.3B_(OPT)≦B_(X)≦0.9B_(OPT) are satisfied.

According to the eleventh aspect of the present invention, in the eighthaspect, B_(X)=1 is satisfied.

According to the twelfth aspect of the present invention, in theseventh, eighth, ninth or tenth aspect, 20≦M≦80, L=6 and D=2 aresatisfied.

According to the thirteenth aspect of the present invention, in theseventh, eighth, ninth or tenth aspect, 40≦M≦100 and B_(X)≦0.7B_(OPT)are satisfied.

According to the fourteenth aspect of the present invention, in thefirst, second, third, fourth, fifth, seventh, eighth, ninth, tenth oreleventh aspect, 24≦M≦40 and B_(X)≦0.75B_(OPT) are satisfied.

In accordance with the present invention, a multiple line addressingdriving is effected with an L number of simultaneously selected rowelectrodes to provide L≠{square root over (M)} where M represents thetotal number of row electrodes for driving a display area and Lrepresents the number of simultaneously selected row electrodes, whereindriving is performed at a driving bias ratio which is deviated towardthe minimum bias ratio at which a driving voltage is the minimum atVR/VC=1 with respect to the optimum bias ratio at which an ON/OFF ratiois the maximum. Accordingly, a low driving voltage is obtainable incomparison with the conventional case where driving is effected by MLAsystem with L={square root over (M)} while the reduction of picturequality is prevented and a practical ON/OFF ratio can be maintained.Thus, a low voltage driving is performed, which was impossible in theconventional driving system.

Further, in the present invention, since driving is performed with theminimum bias ratio (VR/VC)=1, a part of column voltage levels and avoltage level applied to row electrodes can commonly be used, and thenumber of voltage levels necessary to drive the liquid crystal can bereduced. With this, the power source voltage circuit to generate voltagelevels can be simplified and, cost reduction and low power consumptionare obtainable.

In particular, when dummy rows are used, a multiple line addressingdriving is effected with an L number of simultaneously selected rowelectrodes to provide {square root over ((M/L·(L+D)))}≠N where Drepresents the number of dummy rows and N represents the maximummagnifying power of a unit column voltage obtained by a predeterminedmatrix calculation based on display data and scanning voltages appliedto the row electrodes. In this case, when the driving is performed at abias ratio of VR/VC which is deviated toward the minimum bias ratio atwhich a driving voltage is the minimum with respect to the optimum biasratio at which the ON/OFF ratio is the maximum, the same effect can beexpected. Further, in this case, with use of dummy data, the relationbetween image data and column voltage can be determined so as not to usea column voltage series including the maximum column voltage. In thiscase, when selection is repeated on the same simultaneously selectednumber L, the effect for lowering driving voltage is obtainable incomparison with a case without using dummy rows. Further, from theabove-mentioned reason, the number of column voltage levels can bereduced, and accordingly, the power source voltage circuit can besimplified, and reduction of cost and low power consumption can berealized.

Further, since the driving is performed with an L number ofsimultaneously selected rows which satisfies 0.3{square root over(M)}≦L≦2{square root over (M)}, and at a bias ratio in a range of from0.3 times to 0.9 times as much as the optimum bias ratio, apredetermined ON/OFF ratio can be assured regardless of the total numberof electrodes for the display area, and driving is performed with a lowdriving voltage which was impossible to realize in the conventional MLAsystem.

In particular, when the total number of row electrodes for the displayarea is 20-100, and driving is effected with a simultaneously selectednumber of 4 at the minimum bias ratio (VR/VC)=1, the number of voltagelevels necessary to drive the liquid crystal can be reduced in additionto the effect for lowering voltage; the power source voltage circuit forgenerating voltage levels is simplified, and reduction of cost and lowpower consumption are obtainable.

Further, in use of dummy rows, a number of dummy rows satisfyingD/(D+L)<0.5 should be used for driving. There tends to decrease theON/OFF ratio with increasing the number of dummy rows in a case ofdriving using a same simultaneously selected number and a same biasratio. However, with such range, there is no possibility of beingrecognized as reduction of display quality. Further, the lowering ofvoltage is obtainable.

In particular, when driving is performed with a total number of rowelectrodes of display area of 20-80, a simultaneously selected number of6 and a dummy row number of 2, the column voltage level can be reducedin addition to remarkable effect of lowering voltage, whereby the powersource voltage circuit can be simplified. Further, reduction of cost andlow power consumption are realized.

On the basis of the above-mentioned inventions, when driving isperformed under the conditions that the total number of row electrodesfor the display area is 40-100, and a bias ratio which is not more than0.7 times as much as the optimum bias ratio is used for driving, it issufficient to drive with a power source voltage of 5.5 V or lower.Accordingly, unlike the conventional driving method, it is possible toform a power source with a voltage increased by twice even when a buttonbattery is used for driving, and a special reduction of powerconsumption is obtainable. Further, since a ratio of the power sourcevoltage to the maximum value of the column voltage and row voltagesupplied to the liquid crystal is small, a driving circuit for theliquid crystal device can be formed with a standard logic process.

Further, when driving is performed under the conditions that the numberof the total number of row electrodes for the display area is 40-100,and a bias ratio which is not more than 0.6 times as much as the optimumbias ratio is used for driving, it is sufficient to drive with a powersource voltage of 5.0 V or lower. Accordingly, a sufficient margin canbe assured even when there is a temperature variation. Therefore, astandard logic process can be used to form a driving circuit for theliquid crystal display device so as to obtain a stable operation inaddition to the permission of use of a button battery for driving.

Further, when driving is performed under the conditions that the totalnumber of row electrodes for the display area is 24-40 and a bias ratiowhich is not more than 0.75 times as much as the optimum bias ratio isused for driving, it is sufficient to drive with a driving voltage of3.3 V or lower. Accordingly, a button battery can be used for directlydriving, and the structure of the device can be simplified by, forexample, eliminating a voltage increasing circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a block diagram showing a liquid crystal display device andits peripheral portions according to an embodiment of the presentinvention;

FIG. 2 is a diagram showing a MLA voltage waveform and an IAPT voltagewaveform;

FIG. 3 is a diagram showing a relation of a driving voltage to an ON/OFFration in various driving systems;

FIG. 4 is a diagram showing that dummy data are added to actual displaydata in the MLA driving system;

FIG. 5 is a diagram showing curves of scanning voltage and columnvoltage when a relation of a total number of row electrodes and asimultaneously selected number is changed in the MLA system;

FIG. 6 is a diagram showing a result of simulation for driving theliquid crystal display device according to the third embodiment of thepresent invention;

FIG. 7 is a diagram showing a voltage lowering effect to an IAPT methodin each of the systems;

FIG. 8 is a diagram showing a result of simulation for driving theliquid crystal display device according to the fourth embodiment of thepresent invention; and

FIG. 9 is a diagram showing a voltage lowering effect to the IAPT methodin each of the systems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described.

Embodiment 1

FIG. 1 is a structural diagram of the liquid crystal display device andits peripheral devices according to Embodiment 1 of the presentinvention. In FIG. 1, numeral 1 designates a simple matrix liquidcrystal display device (a liquid crystal display device) comprising aplurality of liquid crystal display elements arranged in a matrix form,a plurality of row electrodes arranged along a direction of arrangementof the liquid crystal display elements and a plurality of columnelectrodes arranged along the other direction of arrangement of theliquid crystal display elements wherein a degree of brightness of eachliquid crystal display element can be controlled in response to anaveraged effective voltage applied across a row electrode and a columnelectrode during an effective voltage response time of the liquidcrystal element; numeral 2 designates a row electrode driver forapplying scanning voltages to the plurality of row electrodes for eachgroup consisting of a predetermined L number of simultaneously selectedrow electrodes; numeral 3 designates a column electrode driver forapplying column voltages to the plurality of column electrodes insynchronism with the application of the scanning voltages; numeral 4designates an input port to which image data to be displayed on each ofthe liquid crystal elements are successively input; numeral 5 designatesa memory for memorizing the image data in a state corresponding to thematrix; numeral 6 designates an output port for reading the image dataas an image matrix information for each group of the simultaneouslyselected row electrodes from the memory; numeral 7 designates a scanningvoltage matrix output circuit for outputting a scanning voltage matrixinformation to be applied to the simultaneously selected row electrodes;numeral 8 designates a column voltage matrix generation circuit forconducting matrix operations based on the scanning voltage matrixinformation and the image matrix information to output a result as acolumn voltage matrix information, and numeral 9 designates a timinggeneration circuit for synchronizing the operation of the othercircuits.

The operation will be described.

The image data inputted as serially arranged data into the input port 4are successively stored in the memory in a state corresponding to thematrix of the liquid crystal elements, and then, they are outputted asimage matrix information for each simultaneously selected row electrodegroup through the output driver. In synchronism with this, a columnvoltage matrix information is outputted from the scanning voltage matrixoutput circuit 7 to the row electrode driver 2 and the column electrodematrix generation circuit 8. The column voltage matrix generationcircuit 8 performs matrix operations based on the scanning voltagematrix information and the image matrix information to obtain a result,which is outputted as column voltage matrix information to the columnelectrode driver 3. In synchronism with that the row electrode driver 2applies to the simultaneously selected row electrode groups scanningvoltages in accordance with the scanning voltage matrix, the columnelectrode driver 3 applies to a plurality of column electrodes columnvoltages in accordance with the column voltage matrix. Theabove-mentioned operation is repeated. When the scanning voltages inaccordance with the scanning voltage matrix are applied to all the rowelectrodes, a degree of brightness on each liquid crystal element iscontrolled in response to an effective voltage applied during a time inwhich the repetitive operations are finished (hereinbelow, referred toas a frame period) whereby a picture image base on the image data isdisplayed on the liquid crystal display device 1.

A more concrete example will be described. Formula 1 shows theabove-mentioned scanning voltage matrix wherein “+1” corresponds to+V_(R) and “−1” corresponds to −V_(R). The matrix as shown is called anHadamard's matrix of 4 row·4 column (an orthogonal matrix). Formula 2shows the first image matrix and Formula 3 shows the second image matrixwherein “−1” corresponds to, for example, an ON display, and in thiscase, “1” corresponds to an OFF display. Formula 4 shows a columnvoltage matrix in correspondence with the Formula 2 and Formula 5 showsa column voltage matrix in correspondence with the Formula 3. In theFormulas, “0”, “2”, “4”, “−2” and “−4” respectively show a magnifyingpower of a unit column voltage. To each row electrode, a voltageobtained by multiplying the unit column voltage by any of themultiplying powers is applied provided that in this case, the maximummagnifying power (N) is 4.

The voltages shown in these matrices are applied to a simultaneouslyselected row electrode group and predetermined column electrodes in amanner that “first, voltages shown in the first column in the scanningvoltage matrix are applied, and at the same time, the first row of thecolumn voltage matrix is applied, and then, voltages shown in the secondcolumn in the scanning voltage matrix are applied, and at the same time,the second row of the column voltage matrix is applied, . . . ”. Theabove-mentioned operations are repeated to all matrix elements wherebyan average effective voltage in response to the image matrix is appliedto each of the four liquid crystal elements so that the liquid crystalelement is controlled to have a degree of brightness corresponding tothe average effective voltage.

The average effective voltage is determined so that an effectiveresponse time for the liquid crystal element generally coincides withthe above-mentioned one frame period, i.e., average effective voltageper frame period. $\begin{matrix}\begin{pmatrix}1 & 1 & 1 & {- 1} \\1 & {- 1} & 1 & 1 \\1 & 1 & {- 1} & 1 \\1 & {- 1} & {- 1} & {- 1}\end{pmatrix} & \left( {{Formula}\quad 1} \right) \\\begin{pmatrix}1 \\{- 1} \\1 \\{- 1}\end{pmatrix} & \left( {{Formula}\quad 2} \right) \\\begin{pmatrix}1 \\1 \\1 \\{- 1}\end{pmatrix} & \left( {{Formula}\quad 3} \right) \\{\begin{pmatrix}1 & 1 & 1 & {- 1} \\1 & {- 1} & 1 & 1 \\1 & 1 & {- 1} & 1 \\1 & {- 1} & {- 1} & {- 1}\end{pmatrix}^{t}\begin{pmatrix}1 \\{- 1} \\1 \\{- 1}\end{pmatrix}\begin{pmatrix}0 \\4 \\0 \\0\end{pmatrix}} & \left( {{Formula}\quad 4} \right) \\{\begin{pmatrix}1 & 1 & 1 & {- 1} \\1 & {- 1} & 1 & 1 \\1 & 1 & {- 1} & 1 \\1 & {- 1} & {- 1} & {- 1}\end{pmatrix}^{t}\begin{pmatrix}1 \\1 \\1 \\{- 1}\end{pmatrix}\begin{pmatrix}2 \\2 \\2 \\2\end{pmatrix}} & \left( {{Formula}\quad 5} \right)\end{matrix}$

In Embodiment 1 having the above-mentioned basic structure, the relationbetween a supplied voltage required for the column electrode driver andthe row electrode driver under the conditions described below and theratio of an effective voltage in an ON display time to an effectivevoltage in an OFF display time of the liquid crystal display device(hereinbelow, referred to as an ON/OFF ratio), was examined. Theconditions were such that the number L of simultaneously selected rowelectrodes was 4 and the total number M of row electrodes set in thecolumn voltage matrix generation circuit was 32. Further, the liquidcrystal display device included STN liquid crystal elements having atwist angle of 240°, a refractive index anisotropy of 0.145 and adielectric anisotropy of +24.7, which were arranged in a dot matrix formof 32 rows×240 columns. In the liquid crystal display device, aneffective voltage necessary for driving simultaneously all the rowelectrodes to provide an ON display was 1.2 V.

Concrete waveforms applied in the MAL method are shown in FIGS. 2(a) and2(b). The voltage waveform of row electrode in FIG. 2(a) has +VRcorresponding to +1 and −VR corresponding to −1 according to theelements of an orthogonal matrix, and a voltage amplitude of 2 VR havingzero as the center. The voltage waveform of column electrode in FIG.2(b) has an applied voltage in proportion to an inner product of anelement of the orthogonal matrix and a display element. In the MLAdriving method (where L=4) in the figure, when a voltage correspondingto 4 as the maximum value as a result of calculation is represented by+VC, the column voltage has a voltage amplitude of 2 VC having zero asthe center. From the above, a power source voltage required to drive theliquid crystal (or a driving voltage) should have a power sourceamplitude of 2 VR or 2 VC whichever larger.

Concrete waveforms applied for a line successive driving (hereinbelow,referred to as an IAPT driving method) are shown in FIGS. 2(c) and 2(d).In order to drive the liquid crystal, a power source voltage having anvoltage amplitude of VR+VC which is necessary for the IAPT method isrequired.

FIG. 3 is a diagram showing the relations between a ratio of aneffective voltage in an ON display time to an effective voltage in anOFF display time and a driving voltage in several driving systemswherein the ratio of a row voltage VR to the maximum column voltage VC(hereinbelow, referred to as a driving bias ratio=VR/VC) is graduallychanged. In the figure, MLA (L=4, M=32) indicates a curve obtained inEmbodiment 1; MLA (L=6, D=2, M=36, N=4) indicates a curve obtained inEmbodiment 2; IAPT (M=32) indicates a curve obtained in ComparativeEmbodiment 1; and MLA (L=6, M=36) indicates a curve obtained inComparative Embodiment 2.

As is clear from this relational figure, the curve corresponding toEmbodiment 1 of the present invention extends in a lower right region incomparison with the curves of Comparative Embodiments 1 and 2, fromwhich it is understood that it has the same ON/OFF ratio as ComparativeEmbodiments 1 and 2, and it is possible to drive the liquid crystalelements with a lower driving voltage than that of these ComparativeEmbodiments. In particular, it is possible, on one hand, to drive thedevice with a lower driving voltage at a driving bias ratio which ishigher than VR/VC=1 at which the driving voltage is the minimum andwhich is lower than the optimum bias ratio, and, on the other hand, toprovide a high ON/OFF ratio in comparison with a bias ratio which islower than the minimum bias ratio VR/VC=1, whereby the same display asthe conventional MLA driving system can be obtained. Further, whendriving is performed at the minimum bias ratio VR/VC=1, a part of thecolumn voltage levels and voltage levels to be applied to row electrodescan commonly be used, and the voltage level necessary to drive theliquid crystal can be decreased. With such measures, the power sourcevoltage circuit for generating a voltage level is simplified, and costreduction and low power consumption can be realized.

Embodiment 2

A liquid crystal display device wherein the number L of simultaneouslyselected row electrodes was 6; the total number M of row electrodes setby the column voltage matrix generation circuit was 36; and two dummyrows D, which did not exist in the display area, were provided for eachof the simultaneously selected groups, was prepared. Then, data on thecolumn voltage matrix were adjusted so that the maximum magnifying powerN of the column voltages was at most 4.

This will be described with reference to FIG. 4. The total number of rowelectrodes 36 are divided into subgroups each comprising 6 rows, and anHadamard's matrix of 8 rows and 8 columns as an orthogonal matrix isprepared. On each subgroup, all the column vectors in the Hadamard'smatrix are once applied. On the row electrodes, 6 lines in the 8 roworthogonal matrix are applied to the actual electrodes according topolarities. On the column electrodes, column vectors in the orthogonalmatrix and voltages in response to inner products of display data areapplied. A result of calculation of 6 actual data is shown in FIG. 4(a).When 2 dummy data are determined appropriately in addition to the 6actual data, a result of calculation is shown in FIG. 4(b). In theresult of calculation on the 6 actual data, 7 voltage levels: 6, 4, 2,0, −2, −4, and −6, are required in response to the display data.However, when calculation is conducted with 2 dummy data in addition tothe 6 actual data, only 3 voltage levels: 4, 0 and −4, are required.Further, even when the 6 actual data are changed, a result ofcalculation can be given with 3 values: 4, 0 and −4, by changing thedummy data in response to the actual data. As described above, it ispossible to reduce the number of necessary column voltage levels byusing dummy data in response to actual data, in comparison with a casewithout using dummy data. Namely, the sole use of this method impliesthat the power source voltage circuit for generating voltage levels canbe simplified, and cost reduction and low power consumption can berealized.

4 Rows among 36 rows are not actually applied to the liquid crystaldisplay device.

The structure other than the above-mentioned is the same as that ofEmbodiment 1 and description is therefor omitted.

A result obtained by the operation is shown in FIG. 3. As is clear fromthe figure, in the curve corresponding to Embodiment 2, the minimum biasratio is produced by a further lower driving voltage (2.79 V) incomparison with the case of Embodiment 1, and the ON/OFF ratio at thattime is 1.132. Accordingly, it is possible to provide the same functionas Embodiment 1 and a practically usable ON/OFF ratio while driving canbe performed with a further lower driving voltage than that inEmbodiment 1.

Comparative Embodiment 1

The construction of the liquid crystal display device is the same asthat of Embodiment 1 except that it is adapted to be driven by IAPTdriving system, and therefore, description is omitted.

A result obtained is shown in FIG. 3. As is clear from the figure, inComparative Embodiment 1, the driving voltage Vd tends to decrease in aregion where the ON/OFF ratio is the maximum toward a region having alower ON/OFF ratio. However, it is smaller than the optimum bias ratioof Embodiment 1, and the driving voltage Vd of Comparative Embodiment isalways not lower than the driving voltage of Embodiment 1 in a region ofON/OFF ratio assuming the minimum bias ratio. Similarly, the drivingvoltage Vd of Comparative Embodiment 1 is always not lower than that ofEmbodiment 1 in a region of ON/OFF ratio assuming the minimum bias ratioand smaller than the optimum bias ratio of Embodiment 2.

Comparative Embodiment 2

A liquid crystal display device wherein the number L of simultaneouslyselected row electrodes was 6; the total number M of row electrodes setby the column voltage matrix generation circuit was 36, and a scanningvoltage matrix of 6 row·8 column was set, was prepared. 4 Rows among 36rows were not actually applied to the liquid crystal display device.Other elements are the same as those of Embodiment 1, and description isomitted.

A result is shown in FIG. 3. As is clear from the figure, ComparativeEmbodiment 2 did not show a driving voltage which was lower than theoptimum bias ratio at which the ratio of an effective voltage in an ONdisplay time to an effective voltage in an OFF display time was themaximum. Further, the point providing such ON/OFF ratio is in an upperleft region with respect to the curve of Embodiment 1, and does not showa lower driving voltage at the same ON/OFF ratio. Further, the drivingvoltage Vd of Comparative Embodiment 1 is always not lower in a regionof ON/OFF ratio assuming the minimum bias ratio and smaller than theoptimum bias ratio of Embodiment 2.

FIG. 5 shows the relations between an ON/OFF ratio and a driving voltagewherein the relation between the number L of the simultaneously selectedrows and the number M of the total row electrodes is changed. FIG. 5ashows relationships in a case of 1<L<{square root over (M)}; FIG. 5bshows relationship in a case of L={square root over (M)} and FIG. 5cshows relationship in a case of {square root over (M)}<L wherein VCrepresents a curve indicating the maximum column voltage (=unit columnvoltage×magnifying power N×2) and 2 VR is a curve indicating a scanningvoltage. The curve of Embodiment 1 and the curve of Embodiment 2 asshown in FIG. 2 are respectively obtained in the same manner asobtaining by selecting either the curve indicating the maximum columnvoltage or the curve indicating the scanning voltage, shown in FIG. 5c,whichever is greater in voltage. The curve of Comparative Embodiment 2shown in FIG. 3 can be obtained in the same manner as obtaining byselecting either the curve indicating the maximum column voltage or thecolumn indicating the scanning voltage, shown in FIG. 5b, whichever isgreater in voltage.

Embodiment 3

A liquid crystal display device comprising STN liquid crystal elementshaving a twist angle of 240°, a refractive index anisotropy of 0.145 anda dielectric anisotropy of +24.7, which are arranged in a dot matrixform of 32 rows and 240 columns was used to confirm its operation. Aneffective voltage obtained when all the row electrodes weresimultaneously driven to provide an ON display was 1.2 V.

With use of the liquid crystal display device, simulation on the ON/OFFratio and the driving voltage was conducted. FIGS. 6 and 7 shows a parta result obtained. For comparison, FIG. 6 shows a result in a case thatthe liquid crystal display device is driven by IAPT driving system aswell as a result in a case that the device is driven by the conventionalMLA driving system.

In order to clearly show respective effects of FIG. 6, the voltagelowering effect to the driving voltage in the IAPT method by using thesame ON/OFF ratio (a ratio of effective voltages in ON and OFF displaytimes) is shown in FIG. 7.

As a result, it has been confirmed that when the liquid crystal displaydevice is driven with an L number of simultaneously selected rowssatisfying 0.3{square root over (M)}≦L≦2{square root over (M)} where nodummy is used or an L number of simultaneously selected rows satisfying0.3{square root over (M)}≦L+D≦2{square root over (M)} where a dummy ordummies are used, and when it is driven at the minimum bias ratio ofVR/VC (VR/VC=1), a predetermined ON/OFF ratio can be assured regardlessof the total number of row electrodes for the display area, and thedevice can be driven with a lower driving voltage than that of theconventional multiple line driving system or IAPT driving system.

Further, it has also been confirmed that when the total number M of rowelectrodes used is 24-40 and a bias ratio of 0.75 times or lower thanthe optimum bias ratio is used for driving, a driving voltage of 3.3 Vor lower is sufficient for driving. Under these conditions, accordingly,it is possible to drive directly with use of a button battery. Thestructure of the device can be simplified by omitting a voltage increasecircuit, and a driver circuit for a liquid crystal display device can beformed by using a standard logic process.

It has also been confirmed that when a dummy (dummies) is used, in thiscase, a number of dummies satisfying D/(D+L)<0.5 is used and if drivingis effected at the same driving bias ratio on the same number L ofsimultaneously selected rows, the ON/OFF ratio tends to decrease as thenumber of dummy rows is increased. However, it was confirmed that withsuch range, there was no danger of being recognized as reduction in thedisplay quality, and the power source voltage could be reduced withoutcausing deterioration of the picture quality.

Embodiment 4

A liquid crystal display device comprising STN liquid crystal elementshaving a twist angle of 240°, a refractive index anisotropy of 0.144 anda dielectric anisotropy of +13.6, which were arranged in a dot matrixform of 64 rows and 240 columns, was prepared to confirm its operation.An effective voltage obtained when all the row electrodes weresimultaneously driven to provide an ON display, was 1.55 V.

With such liquid crystal display device, simulation was conducted on theON/OFF ratio and the driving voltage. FIGS. 8 and 9 show a part of aresult by the simulation. For comparison, FIG. 8 shows, in parallel, aresult obtained by driving the liquid crystal display device by theconventional MLA driving system.

In order to clearly show respective effects of FIG. 8, the voltagelowering effect to the driving voltage on the IAPT driving method byusing the same ON/OFF ratio is shown in FIG. 9.

As a result, it has been confirmed that when the device is driven withan L number of simultaneously selected rows satisfying 0.3{square rootover (M)}≦L≦2{square root over (M)} in a case of using no dummy, or whenthe device is driven with an L number of simultaneously selected rowssatisfying 0.3{square root over (M)}≦L+D≦2{square root over (M)} in acase of using a dummy (dummies) wherein driving is performed at theminimum bias ratio of VR/VC (VR/VC=1), driving can be achieved with alower driving voltage than that in the conventional MLA driving systemor IAPT driving system while a predetermined ON/OFF ratio can be assuredirrespective of the total number of row electrodes for the display area.

In particular, it has been confirmed that when the total number of rowelectrodes for the display area is 40 to 100 and a bias ratio used fordriving is at most 0.7 times as much as the optimum bias ratio, a powersource voltage of at most 5.5 V is sufficient to drive the liquidcrystal display device. Also, it has been confirmed that the powersource voltage is increased by twice to thereby lower remarkably powerand a driver circuit for the liquid crystal display device can be formedby using a standard logic process.

Further, it has been confirmed that when the total number of rowelectrodes for the display area is 40 to 100 and driving is performed ata bias ratio of at most 0.6 times as much as the optimum bias ratio, apower source voltage of at most 5.0 V is sufficient. Also, it has beenconfirmed that use of a button battery or the like is allowed fordriving and a driver circuit for the liquid crystal display device canbe formed by using a standard logic process to obtain a stable operationsince a sufficient margin can be maintained even in a case oftemperature variation.

When a dummy (dummies) is used and if driving is performed with a numberof dummies satisfying D/(D+L)<0.5 at the same driving bias ratio on thesame number L of simultaneously selected rows, the ON/OFF ratio tends todecrease as the number of dummy rows is increased. However, it has beenconfirmed that with such range, there is no danger of being recognizedas reduction in the display quality while the power source voltage canbe reduced without causing deterioration of the picture quality.

What is claimed is:
 1. A method for driving a simple matrix liquidcrystal display device characterized by conducting a multiple linedriving with an L number of simultaneously selected row electrodes toprovide L≠{square root over (M)} where M represents the total number ofrow electrodes for driving a display area and L represents the number ofsimultaneously selected row electrodes, wherein driving is performed ata bias ratio which is deviated toward the minimum bias ratio at which adriving voltage is the minimum with respect to the optimum bias ratioB_(OPT) at which a ratio of an effective voltage value in an ON displaytime to an effective voltage value in an OFF display time is themaximum.
 2. The method for driving a simple matrix liquid crystaldisplay device according to claim 1, wherein the display area is dividedinto subgroups each comprising L lines; column elements selected in anorthogonal matrix of L lines composed of +1 and −1 are madecorresponding to each line of the subgroups; row voltage levels where +1corresponds to +VR and −1 corresponds to −VR are applied to each rowelectrode of the subgroups; inner products are obtained from an L numberof column data elements, having a value −1 in an ON display time or +1in an OFF time, which intersect a certain row electrode and columnelements in the orthogonal matrix of L lines; predetermined columnvoltages in proportion to the inner products are applied to columnelectrodes in synchronism with the row electrodes, a bias ratio B_(X)given by VR/VC where VC represents the maximum column voltage satisfies1≦B_(X)≦B_(OPT).
 3. The method for driving a simple matrix liquidcrystal display device according to claim 1, wherein 0.3{square rootover (M)}≦L≦2{square root over (M)} and 0.3B_(OPT)≦B_(X)≦0.9B_(OPT) aresatisfied.
 4. The method for driving a simple matrix liquid crystaldisplay device according to claim 1, wherein 40≦M≦100 andB_(X)≦0.7B_(OPT) are satisfied.
 5. The method for driving a simplematrix liquid crystal display device according to claim 1, whereinB_(X)=1 is satisfied.
 6. The method for driving a simple matrix liquidcrystal display device according to claim 1, wherein 20≦M≦40 and L=4 aresatisfied.
 7. A method for driving a simple matrix liquid crystaldisplay device characterized by conducting a multiple line addressingsystem with an L number of simultaneously selected row electrodes toprovide {square root over ((M/L·(L+D)))}≠N where M represents the totalnumber of row electrodes for driving a display area, L represents thenumber of simultaneously selected row electrodes, D represents a numberof dummy row electrodes and N represents the maximum magnifying power ofa unit column voltage obtained by a predetermined matrix calculation todisplay data and scanning voltages applied to the row electrodes,wherein driving is performed at a driving bias ratio which is deviatedtoward the minimum bias ratio at which a driving voltage is the minimumwith respect to the optimum bias ratio B_(OPT) at which a ratio of aneffective voltage value in an ON display time to an effective voltagevalue in an OFF display time is the maximum.
 8. The method for driving asimple matrix liquid crystal display device according to claim 7,wherein the display area is divided into subgroups each comprising Llines; column elements selected in an orthogonal matrix of L+D linescomposed of +1 and −1 are made corresponding to each line of thesubgroups; row voltage levels where +1 corresponds to +VR and −1corresponds to −VR are applied to each row electrode of the subgroups;an L number of column data elements intersecting a certain row electrodeare represented as −1 in an ON display time or +1 in an OFF time and a Dnumber of dummy data are made corresponding to column data elements toprepare an L+D number of column data elements; inner products areobtained from such column data elements and column elements in theorthogonal matrix of L+D lines; predetermined column voltages inproportion to the inner products are applied to column electrodes insynchronism with the row electrodes; L which satisfies {square root over((M/L·(L+D)))}≠N where N represents the maximum magnifying power of aunit column voltage obtained by a predetermined matrix calculation todisplay data and scanning voltages applied to the row electrodes, amaximum value of the inner products, and a bias ratio B_(X) given byVR/VC where VC represents the maximum column voltage satisfies1≦B_(X)<B_(OPT).
 9. The method for driving a simple matrix liquidcrystal display device according to claim 7, wherein 0.3{square rootover (M)}≦L+D≦2{square root over (M)} and 0.3B_(OPT)≦B_(X)≦0.9B_(OPT)are satisfied.
 10. The method for driving a simple matrix liquid crystaldisplay device according to claim 7, wherein D/(D+L)<0.5 is satisfied.11. The method for driving a simple matrix liquid crystal display deviceaccording to claim 8, wherein B_(X)=1 is satisfied.
 12. The method fordriving a simple matrix liquid crystal display device according to claim7, wherein 20≦M≦80, L=6 and D=2 are satisfied.
 13. The method fordriving a simple matrix liquid crystal display device according to claim7, wherein 40≦M≦100 and B_(X)≦0.7B_(OPT) are satisfied.
 14. The methodfor driving a simple matrix liquid crystal display device according toclaim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein 24≦M≦40 andB_(X)≦0.75B_(OPT) are satisfied.